In this study, a dual effect of enhancing joint strength in 2A12 aluminum alloy and reducing energy consumption is achieved by the addition of trace carbon nanotubes

The widespread use of laser welded aluminum alloys in industrial production offers potential benefits to sustainable development and socio-economic progress. It simultaneously enhances the weld strength while reduces the energy consumption. Despite the promise of these alloys, research on reducing their energy consumption during laser welding is lacking. In this study, a dual effect of enhancing joint strength in 2A12 aluminum alloy and reducing energy consumption is achieved by the addition of trace carbon nanotubes (CNTs). The "welding efficiency" is defined and an energy consumption model for laser welding of aluminum alloys is developed.

Next, the laser welding process with the addition of trace CNTs (LC) and the single laser welding process (LW) were compared and analyzed. The results indicate that adding trace CNTs can reduce energy consumption by more than 33 % and increase joint strength by 101 MPa. Furthermore, it is found that the LC process offers significant energy-saving advantages over other laser welding of aluminum alloy processes described in previous studies. These improvements is attributed to the increased laser absorption by the aluminum alloy induced by trace CNTs, as well as their residual presence in the joint, which acts as a strengthening medium. This work provides new insights and presents a novel approach for achieving low-carbon, high-quality welding of aluminum alloys.

Introduction

Industrial production, which converts materials, energy, and labor into goods and services generates a significant amount of environmental emissions (R.U. Ayres and Simones, 1994). Energy consumption statistics from the past decade indicate that industrial production accounts for 20 %–30 % of energy consumption. This makes it the most in need of reform for international sustainable development (International Energy Agency, 2012, 2017). Welding, as an essential component of industrial production, has gradually garnered social attention due to its production efficiency and environmental impact. Some studies have even hypothesized that reducing the energy consumption of arc welding processes by 1 % per year could save over 2 billion kW of electricity (Yan et al., 2017). High-strength 2A12 aluminum alloy is widely used in wing ribs, lightweight ships, home building materials and automobiles (Li et al., 2021; Sun et al., 2019). The extensive use of aluminum alloys has replaced some steel materials and achieved environmentally friendly development through weight reduction (Hong and Shin, 2017).

In these applications, there are many cases of connecting aluminum profiles through welding. At the same time, the accelerated development of high-power lasers has gradually dominated the field of welding for aluminum alloys (Xu et al., 2022a). Meanwhile，the increasing energy cost and environmental impact makes the development of more efficient laser welding an urgent priority. However, current research primarily focuses on welding performance and microstructure. This lacks optimal solutions and considerations for reducing energy consumption in laser welding.

To reduce the energy consumption of laser welding of aluminum alloys, it requires not only theoretical guidance from carbon emission or energy consumption models, but also concrete experiments to validate and optimize the welding process and energy consumption models. In terms of the former, research has provided thermal wire laser welding energy efficiency evaluation models based on process characteristics and power consumption. It is found that thermal wire welding can save up to 16 % more energy than cold wire welding (Wei et al., 2015). In addition, various oscillating laser welding energy efficiency models have also been reported (Le-Quang et al., 2021). Some studies have guided the distribution of welding energy from a pure mathematical model perspective, thereby improving the utilization efficiency of welding energy (Goffin et al., 2021). These works were expected to help guide corresponding laser welding processes. However, these energy efficiency models are specific to certain laser welding processes and are not universal. Currently, the most widely used single laser welding lacks an energy efficiency evaluation mechanism. Moreover, it is more practical for the environment and economy to explore the feasibility of single laser welding processes to reduce the energy consumption.

Among various welding methods, laser welding has outstanding advantages such as high cleanliness, high energy density, and small heat-affected zones (Cui et al., 2018; Xu et al., 2022c). This is also a critical factor that distinguishes laser welding in joining aluminum alloys. Studies have compared the carbon emissions of three processes, namely laser, arc, and laser-arc hybrid welding. It is found that laser welding has the lowest energy consumption and carbon emissions (Wu et al., 2022). However, aluminum and copper alloys often waste a significant amount of laser energy due to their high reflectivity as compared to steel, titanium alloys and high entropy alloys (Liang et al., 2020). Therefore, improving the laser absorptivity of aluminum alloys without changing their chemical composition is an effective way to overcome the bottleneck of energy wastage in welding.

Coincidentally, CNTs have a naturally porous and pure black light-absorbing property. Furthermore, numerous studies have shown that CNTs are ideal aluminum alloy reinforcements due to their excellent mechanical and thermodynamic properties (Popov, 2004; Yu et al., 2000). Based on this, depositing CNTs on the welding surface becomes a robust measure to solve the high reflectivity of aluminum alloys and improve energy utilization efficiency. Importantly, this approach does not sacrifice the mechanical performance of the joint.

In this study, the characteristics of enhancing the laser absorption rate of aluminum alloy using CNTs were utilized. Laser welding process with the addition of trace CNTs (LC) and the single laser welding process (LW) experiments were carried out, and multi-dimensional comparative studies were conducted on welding efficiency, welding energy consumption, and joint strength. Specifically, the welding efficiency and single laser welding energy consumption model were established. Then, the energy consumption and welding efficiency of laser welding processes with and without the addition of CNTs were compared. In addition, to highlight the advantages of the LC process in saving welding energy, the results were compared with various laser welded aluminum alloys reported in the literature. The mechanism of improving welding efficiency and reducing the energy consumption of the LC process was also discussed and analyzed. Finally, the tensile strength of the LC and the LW joints was compared. This work provides a competitive solution for low-carbon, high-quality laser welding of aluminum alloys.

Conclusion

In this study, the addition of trace CNTs significantly improved the efficiency of laser welding of aluminum alloys and reduced welding energy consumption. Firstly, the LW and the LC processes were compared and analyzed using energy consumption and welding efficiency models. In addition, the LC-3 process was compared with the laser energy consumption of related work. The mechanical performance, as an important indicator of welding, was also involved in the evaluation of each joint.

Simultaneous Reduction In Laser Welding Energy Consumption And Strength Improvement Of Aluminum Alloy Joint By Addition Of Trace Carbon Nanotubes